#define _CRT_SECURE_NO_WARNINGS  1

#include<stdio.h>

int main()
{
	int n = 0;
	scanf("%d", &n);
	int i = 0;
	int sum = 0;
	int j = 2;
	for(i=0;i<n;i++)
	{
		sum=sum+j;
		j=j+3;
	}
	printf("%d",sum);
	return 0;
}